Prognostication of future failure of an engine indicator parameter

ABSTRACT

Power spectral densities are taken at periodic intervals for preselected indicator parameters and these power spectral density profiles are compared to a reference magnitude of a power spectral density profile for purposes of prognosticated future failures. The power spectral density profile can be for any one of a plurality of indicator profiles, such as an accelerometer output, the output of a pressure sensor, or a voltage output from an ignition system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to a means for characterizingthe operation of an apparatus and prognosticating a condition of anapparatus and, more particularly, to a method by which a marinepropulsion system can be monitored in order to both diagnose its currentoperating condition and to predict future failures before they becomecatastrophic.

2. Description of the Prior Art

In any complex system or apparatus, it is often desirable to monitorcertain parameters to determine if the apparatus is operating in aproper manner. For example, in an automobile, oil pressure and coolanttemperature are monitored continually. If oil pressure drops below apredetermined threshold magnitude, an alarm signal is provided to informthe operator that low oil pressure exists and continued operation of theautomobile under these conditions could be severely damaging to theengine. Similarly, coolant temperature is monitored and compared to apredetermined threshold magnitude. When the coolant temperature exceedsthe predetermined threshold, an alarm signal is provided to the operatorof the automobile that continued operation under the overheatedconditions could result in severe damage to the engine. These operatingconditions are relatively straightforward and easily monitored. In bothexamples, the alarm signal represents a present situation that requiresimmediate attention. In other words, the overtemperature alarm does notindicate that a potential future overtemperature condition may occurbut, instead, it indicates that the coolant temperature is presentlygreater than the predetermined temperature threshold. Similarly, the lowpressure alarm does not predict a low pressure in the future but,instead, represents an existing condition in which the oil pressure iscurrently lower than required for proper operation of the engine.

Many techniques have been developed to monitor operating equipment andpredict future failures that are not readily apparent and not easilydetectable by basic monitoring techniques.

U.S. Pat. No. 5,633,456, which issued to Stander on May 27, 1997,describes an engine misfire detection system with digital filtering. Theapparatus and method provide for detecting cylinder misfires in aninternal combustion engine of a motor vehicle by digitally filtering outnoise related signals to improve the signal to noise ratio. Crankshaftrotation is sensed and crankshaft velocities are measured for eachcylinder. Changes in angular velocity are determined and correspond toeach of a plurality of cylinder firing events. A window of consecutivechanges in angular velocity are used with a digital filter. The digitalfilter contains filter coefficients which are determined from afrequency analysis for a given engine by distinguishing between actualmisfire events and noise related event frequencies. From the analysis, acut off frequency between actual misfires and noise is determined whichis then used to determine the filter coefficients. The digital filtergenerates a filter output for the current cylinder firing event and thefilter output is preferably multiplied by a gain to provide to provide acompensated filter output. The compensated filter output is compared toa threshold value and a misfire event is determined for the selectedcylinder based on the comparison. A high pass filter may be employed tofilter out low frequency noise related signals such as those associatedwith a power train bobble. Similarly, a low pass filter can be used tofilter out high frequency noise signals such as those associated withcrankshaft torsional vibrations. Both high and low pass filters could beemployed in the alternative by using a high pass filter at low enginespeeds and a low pass at high engine speeds.

U.S. Pat. No. 5,745,382, which issued to Vilim et al on Apr. 28, 1998,describes a neural network based system for equipment surveillance. Themethod and system is provided for performing surveillance of transientsignals of an industrial device to ascertain the operating state. Themethod and system involves the steps of reading into a memory trainingdata and determining neural network weighting values until achievingtarget outputs close to the neural network output. If the targetsoutputs are inadequate, wavelet parameters are determined to yieldneural network outputs close to the desired set of target outputs andthen providing signals characteristic of an industrial process andcomparing the neural network output to the industrial process signals toevaluate the operating state of the industrial process.

U.S. Pat. No. 5,852,793, which issued to Board et al on Dec. 22, 1998,describes a method and apparatus for predictive diagnosis of movingmachine parts. It is intended for automatically predicting machinefailure and comprises a transducer sensor, such as piezoelectriccrystal, and is applied to a machine for sensing machine motion andstructure-borne sound, including vibration friction, and shock waves.The structure-borne sound and motion sensed is converted to electricalsignals which are filtered to leave only the friction and shock waves,which waves are processed, as by detecting the envelope and integratingbeneath the envelope, resulting in a measure of friction and shock waveenergy. This measure is computed and processed for producing faultprogression displays for periodic and aperiodic damage. This isaccomplished in a personal computer, menu-driven environment.

U.S. Pat. No. 5,646,340, which issued to Gee et al on Jul. 8, 1997,describes an analytical tachometer. The method and apparatus for engineand rotary machine analysis provides a vibration sensor adapted toproduce a plurality of superimposed waveforms corresponding to engine ormachine operating parameters including rotational speed. The signals aretransmitted by an RF transmitter/receiver system in analog modulatedform to a data capture and analytical function unit utilizing a softwaresub-system in which a power spectral density plot is produced containinga signature characteristic of the engine or other machine under test.This signature is recognized by a signature detect algorithm which canrecognize and trace the signature across the frequency spectrum coveredby the apparatus so as to provide a continuous tachometric function notrequiring the filtering out or other removal of irrelevant data. Adiagnostic function arises from detection of the presence of additionalharmonic peaks within the signature. A capacitive coupling offers asimplified tachometric function based upon low voltage signals in theinjector leads of a spark ignition engine.

The patents described above are hereby explicitly incorporated byreference in the present application.

In the second edition of “RANDOM DATA, ANALYSIS AND MEASUREMENTPROCEDURES” by Bendat and Piersol, published by John Wiley & Sons,paragraph 6.1.2 describes ordinary coherence functions in relation topower spectral densities. In addition, it describes an example of anapplication of a power spectral density with regard to an airplaneflying through atmospheric turbulence. The application of power spectraldensity profiles and the integrals thereof are generally known to thoseskilled in the art. Coherence functions can be used to distinguishbetween a reference power spectral density profile and a current powerspectral density profile to determine whether or not the differencesbetween the two are normal variations or, alternatively, represent anactual difference between the two profiles.

In certain mechanical apparatus, it would be significantly beneficial ifa means could be provided that would allow the prognostication of faultsbefore the faults become catastrophic or disabling. This is especiallytrue in marine propulsion systems. If a system could be provided thatpredicted failure of mechanical or electrical components before thosefailures actually occurred, the problem components could be repaired orreplaced and the failure of the components would not result in themarine vessel operator being stranded and unable to return to port. Ifan automobile engine fails, the driver is usually able to obtainalternative means of transportation that would allow the operator toreturn home safely and repair the automobile at some future time. Inmarine propulsion system applications, it is often the case that themarine vessel can be far from either the nearest convenient port orother vessels when an engine failure or other mechanical failure occurs.If the failure occurs when the marine vessel is far from land,alternative means for the operator to return to port may not be readilyavailable. It would therefore be significantly beneficial if failurescould be predicted sufficiently before their actual occurrences to allowthe marine vessel operator to correct the problem before it occurs.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a method forprognosticating a potential failure condition of an apparatus whichcomprises the steps of determining a reference magnitude of an indicatorparameter under a first set of preselected conditions and storing thereference magnitude of the indicator parameter for later use. Theindicator parameter can be, but is not limited to, a g-force valueprovided as an output from an accelerometer attached to a gearcase of amarine propulsion unit or another location of a marine propulsionsystem, a pressure value provided by a pressure sensor connected to theoil system, fuel system, or air delivery system of an engine, or signalsreceived by an ignition system of an engine. The reference magnitude ofthe indicator parameter can be developed by monitoring the indicatorparameter for a preselected period of time and obtaining an operatingmean value that is used as the reference magnitude. The first set ofpreselected conditions can include engine speed, measured in revolutionsper minute (RPM). Additionally, it can also include a engine torque,measured in foot pounds. The reference magnitude can be stored in thememory of a micro-processor.

In a particularly preferred embodiment of the present invention, thefirst set of preselected conditions includes both engine speed (RPM) andengine load and these two operating characteristics are divided into aplurality of magnitude ranges. For each magnitude range of both theengine speed and the engine load, a unique reference magnitude is storedfor the indicator parameter.

In a particularly preferred embodiment of the present invention, thereference magnitude is a power spectral density (PSD) profile, as afunction of frequency, that is completely or partially stored as thereference magnitude.

The present invention further comprises the step of measuring thecurrent magnitude of the indicator parameter under the first set ofpreselected conditions.

The current magnitude is measured subsequent to the reference magnitudebeing determined. In other words, after the reference magnitude of theindicator parameter is stored as a function of the engine speed andengine load, for example, it is compared to a current reading of thesame indicator parameter. The current magnitude is then compared to thereference magnitude. By comparing the reference and current magnitudesof the indicator parameter, such as the power spectral density (PSD) orthe integral of the power spectral density, in part or totally, a changein the condition of the apparatus can be detected.

In a preferred embodiment of the present invention, the measuring,comparing, and detecting steps are repeated continually at apredetermined frequency so that the current condition or magnitude ofthe indicator parameter can be continually compared to the referencemagnitude of the indicator parameter. This enables the operatingcondition of the apparatus to be continually monitored in a way thatallows for prognostication of potential future failures.

A preferred embodiment of the present invention would typicallydetermine the reference magnitudes of each of the plurality of indicatorparameters under an associated first set of preselected conditions foreach of the plurality of indicator parameters. In other words, the powerspectral density (PSD) for an accelerometer output, a pressuretransducer output, and a voltage output from an ignition system couldall be monitored by the present invention. Each of these differentindicator parameters would have a reference magnitude, or profile,stored as a function of one or more operating conditions. For example,they can be stored as power spectral densities or the integrals of powerspectral densities related to the indicator parameters and stored as afunction of either engine speed alone, engine speed in combination withengine load, or any other operating characteristics.

Another embodiment of the present invention provides a method forcharacterizing the operation of an apparatus. The method comprises thesteps of monitoring the magnitude of a first operating condition andperiodically measuring a first indicator parameter during a time whenthe apparatus is operating at the first magnitude of the first operatingcondition. This embodiment of the present invention also comprises thestep of recording an accumulated duration of time that the apparatus hasoperated at a first magnitude of the first operating conditions. Forexample, if the first operating condition is engine speed, the presentinvention would record the accumulated duration of time at each of theplurality of ranges of engine speed. More specifically, the number ofminutes that the apparatus operates at an engine speed between 3000 RPMand 3500 RPM could be accumulated and each range of 500 RPM from 0 RPMto a maximum magnitude would be maintained in this same manner. Thisrecording of the accumulated duration of time at a plurality of rangesof the first operating conditions allows an operational profile to bemaintained.

The present invention would then determine a reference magnitude of afirst indicator parameter for subsequent use when the apparatus isoperating at the first magnitude of the first operating condition. Thereference magnitude is determined as a function of one or moremeasurements of the first indicator parameter. In other words, thepresent invention periodically measures the first indicator parameterand develops a reference magnitude as a function of those measurements.The reference magnitude is stored as a function of the engine speedrange at which the measurements were taken. Naturally, it should beunderstood that the first operating condition of the apparatus does nothave to be engine speed. It can also be engine load or engine speed andengine load in combination.

The present invention further comprises the step of comparing theaccumulated duration of time at the first operating condition to apredetermined threshold magnitude. The predetermined threshold magnitudecan be virtually any magnitude of time, such as 20 minutes, that allowsthe present invention to have a sufficient degree of confidence that thereference magnitude is reliable. The present invention further comprisesthe step of calculating a difference between the stored referencemagnitude and a subsequent measurement of the first indicator parameter.This indicator parameter, as described above, can be a power spectraldensity (PSD) or the integral of a power spectral density relating to anaccelerometer output, a pressure transducer output, a voltage outputfrom an ignition system of the apparatus, or a voltage output from afuel or air injector. The present invention also comprises the step ofprovided an output signal if the difference between the stored referencemagnitude and the subsequent measurement of the first indicatorparameter exceeds a preselected value. The provision of the outputsignal can also be conditional on the comparison of the accumulatedduration of time at the first operating condition and a predeterminedthreshold magnitude. For example, if the apparatus is an engineoperating at a particular engine speed under a particular load, but theapparatus had not operated under these two simultaneous conditions for aminimum time duration of at least 20 minutes, the output signalproviding step can be ignored if the value is below a predeterminedlimit. If, however, the engine had been operated at the combination ofengine speed and engine load for greater than the minimum time duration(i.e. 20 minutes), the output signal can be used as an alarm conditionbecause the reference magnitude stored as a function as the currentengine speed and engine load would represent an operating value in whichsufficient confidence could be placed to determine that the apparatus isnot operating properly.

In summary, the present invention provides a method for judging theacceptability of an indicator parameter by comparing a recent magnitudeof the indicator parameter to a stored reference magnitude of the sameindicator parameter. The indicator parameter is a power spectral densityor the integral of a power spectral density relating to a preselectedvariable, such as an accelerometer output, a pressure transducer output,or a voltage signal. In certain instances, a particular frequency rangeof a power spectral density or the integral of a power spectral densityis used if that particular range has been predetermined to beparticularly indicative of a fault condition. The present invention alsodevelops an accumulative duration of time of the apparatus at specificmagnitudes of certain operating conditions and uses that profilerelationship to determine whether or not a particular indicatorparameter should be used as a reference magnitude for any particularcombination of operating conditions, such as engine speed and engineload.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully and completely understood froma reading of the description of the preferred embodiment in conjunctionwith the drawings, in which:

FIG. 1 is a hypothetical graphical representation of a reference profileand a subsequently taken profile for an indicator parameter;

FIG. 2 is a simplified schematic of a system that can be used to performthe present invention;

FIG. 3 shows four power spectral density profiles for two good gearsets, a spalled gear set, and a bad gear set;

FIG. 4 shows an integral version of the profiles of FIG. 3;

FIG. 5 shows six power spectral density profiles for variouscombinations of good gear sets, spalled gear sets, bad gear sets,undamaged propellers, and damaged propellers;

FIG. 6 shows power spectral densities for a damaged and an undamagedpropeller;

FIG. 7 shows six power spectral density profiles that represent variouscombinations of good gears, spalled gears, bad gears, undamagedpropellers, and damaged propellers;

FIG. 8 shows the power spectral density profiles for an ignition systemat idle, an ignition at 1800 RPM, and an ignition system at 4000 RPM;

FIG. 9 shows three power spectral density profiles for ignition traceswhich are normal, having a fouled plug, and having a worn plug;

FIG. 10 shows power spectral density profiles for an ignition systemthat is normal, having a bad coil, having a struck air injector, havingan overly lean fuel/air mixture, and having a degraded injector;

FIG. 11 shows integral power spectral density profiles of an ignitionsystem that is normal, having a bad coil, having a struck air injector,having an overly lean fuel/air mixture, and having a degraded injectorwhich was simulated by retarding the start of air parameter of the fuelinjection system by 7 degrees;

FIG. 12 shows four power spectral density profiles for fuel pressuremeasurements that indicate a normal injector at idle speed, a struckinjector at idle speed, a normal injector at 4000 RPM, and a stuckinjector at 4000 RPM;

FIG. 13 shows the integral forms of the profiles in FIG. 12;

FIG. 14 shows power spectral densities for air pressure signals at anormal condition, with a struck air injector, and with a simulateddegraded injector;

FIG. 15 shows the integral versions of the profiles of FIG. 14;

FIG. 16 shows a time based representation of an air injector voltage;

FIG. 17 shows a power spectral density of an air injector voltage for agood injector and a stuck injector;

FIG. 18 is a flow chart used to perform the method of a preferredembodiment of the present invention;

FIG. 19 shows a time duration profile as a function of two particularengine operating characteristics;

FIG. 20 shows the three dimensional profile of FIG. 19 with a thresholdplane included; and

FIG. 21 is a flow chart of the method of one of the preferredembodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Throughout the description of the preferred embodiment of the presentinvention, like components will be identified by like referencenumerals.

In order to predict a future failure of components within an apparatusor system, the present invention monitors the power spectral density(PSD) of certain signals provided by certain sensors strategicallyplaced throughout a marine propulsion system. It has been determinedthat the power spectral density can be used to identify subtle changesin the operation of certain components within a marine propulsionsystem.

FIG. 1 shows a hypothetical PSD profile 10 of the power spectral density(PSD) of a selected variable as a function of frequency. Although theprofile 10 in FIG. 1 is hypothetical and provided only for the purposeof explaining the basic concepts of the present invention, it should beunderstood that the preselected variable selected as an indicatorparameter can be the output from an accelerometer, the output from apressure transducer, the reflected signal of a secondary winding voltageof an ignition coil back to the primary winding, or any other transduceroutput. By periodically measuring the power spectral density (PSD) ofthe selected indicator parameter, a reference profile, or magnitude, canbe developed. The profile 10 represented by a solid line in FIG. 1 is ahypothetical reference magnitude for purposes of this description. Itmight be determined that a particular frequency range R of the PSDprofile is particularly indicative of a certain type of mechanical orelectrical failure. This type of behavior is determined throughempirical and theoretical study of a particular system or apparatus. Asan example, it may be determined that a change in the PSD withinfrequency R is a precursor of a gear tooth failure within a powertransmission system. Once the precursor frequency range R is determined,a monitoring system continually measures the power spectral density andprovides a profile of the power spectral density as a function offrequency, at least for the frequency range R. The reference profile 10is then stored for later comparison to periodically update currentmagnitudes of the PSD. Dashed line 12 in FIG. 1 represents the mostcurrent PSD profile for the selected indicator parameter. As can beseen, a comparison of the reference magnitude profile 10 to the mostcurrent PSD profile 12, for the magnitudes within frequency range R,clearly indicate that a change has occurred. A micro-processor which isconnected in signal communication with the appropriate equipment toreceive the date represented graphically in FIG. 1 within determined thedifference between the reference magnitude 10 and the most current PSDprofile 12 within range R and compare the magnitude difference to apredetermined allowable differential. If the calculated differenceexceeds the allowed differential, an alarm condition can be signal tothe operator of the apparatus.

It should be understood that FIG. 1 illustrates a hypothetical referencemagnitude profile 10 and a hypothetical most current PSD profile 12 forthe purpose of describing the basic concept of the present invention anddoes not actually represent empirical data for any indicator parameter.

FIG. 2 is a highly simplified schematic of a system used to implementthe present invention. A micro-processor 20 is provided with memorystorage 22, a means for comparing values 24, an analog to digitalconverter, and logic to provide a condition change detector 26 thatresponds to the mathematical determination of the comparitor 24 incomparing a most current magnitude of a power spectral density with areference magnitude for the same indicator parameter. A system whichincorporates the present invention can also comprise an accelerometer28, a fuel pressure sensor 30, an ignition coil sensor 32, an airpressure sensor 34, and an oil pressure sensor 36. It should beunderstood that the systems can incorporate the present inventionwithout all of the sensors shown in the right side of FIG. 2. Each ofthe sensors, 28, 30, 32, 34, and 36, would provide a signal to themicro-processor 20 that represents a magnitude of an indicatorparameter. For example, the accelerometer can be attached to a gearhousing in which two or more gears are connected in meshing relationwith each other. In addition, the accelerometer could be used to detectthe damaged marine propeller. The fuel pressure sensor could beconnected to an engine's fuel system to detect potential problems withfuel injectors. The ignition coil sensor 32 could be connected in signalcommunication with an ignition coil to monitor the PSD of a voltagesignal emanating from the ignition system. The air pressure sensor 34could be connected in signal communication with an air supply line andcould be used to detect possible problems with an air injection portionof a fuel injector. An oil pressure sensor 36 could be connected insignal communication with an oil delivery system to detect problems withan oil pump or other components of the oil As delivery system. As willbe described in greater detail below, any one or more of the sensorsshown in FIG. 2 can be used to provide a signal for which the powerspectral density can be developed and monitored for use as aprognosticator of potential future failures.

Below, numerous examples of PSD monitoring techniques will be describedin conjunction with associated figures. It should be understood that theparticular PSD used to monitor an indicator parameter will typically bedifferent for each specific apparatus or system that is monitored. Theselection of the indicator parameter in most cases is applicationdependent.

FIG. 3 shows four PSD profiles associated with a gear case of a marinepropulsion system. To measure vibration, an accelerometer was mounted onthe gearcase, near the pinion and forward gears. The accelerometer wasmounted to the gearcase to provide data which demonstrates the magnitudeand frequency distribution changes between a good gear and pinion set incomparison with a spalled gear combination and a bad gear combination.The data represented by the profiles in FIG. 3 was provided by runningthe marine propulsion system with the good gear set, to provide a baseline, and then installing and running the spalled gear set and, later,the bad gear set with a chipped tooth. Then, to verify the base lineresult of the operation with the good gear set, the good gear set wasreinstalled and run again. The spalled gear set had been used for asignificant period of time, and showed spalling, but did not show anyactual damage such as a chipped tooth. The bad gear set actually had achipped tooth. It should be noted, however, that even the chipped geartooth set did not alter the operation of the marine propulsion systemssufficiently to be noticed by the operator. In FIG. 3, lines 41 and 42represent the power spectral densities for runs with good gear sets.Line 43 represents the power spectral density for a spalled gear set andline 44 represents the power spectral density for a bad gear set with achipped gear tooth. Several characteristics of the profiles, 41-44, inFIG. 3 can be noted. First, at frequencies from 0 to approximately 15KHz, the profiles are essentially undistinguishable from each other. Atfrequencies above approximately 21 KHz, line 43 again becomesessentially undistinguishable from lines 41 and 42. Above a frequency ofapproximately 30 KHz, the four lines again become essentiallyundistinguishable from each other. However, in a frequency range of 15KHz to 20 KHz, the spalled 43 and bad 44 gear profiles are clearlydistinguishable from the two good profiles, 41 and 42. Therefore, if thePSD's shown in FIG. 3 are monitored by the present invention, using anindicator parameter which is the output of an accelerometer, spalled andbad gears can be identified by monitoring the frequency range between 15KHz and 20 KHz. The profiles in FIG. 3 represent the power spectraldensity of the vibration, or g force, in the port-starboard direction atapproximately 4,000 RPM. It should be noticed that additional energy inthe range from 15 KHz to 20 KHz is evident for these spalled and badgears. This indicates that there is notably more energy at thesefrequencies as a result of the reduced gear mesh caused by the spallingand chipped tooth.

The same data represented by the profiles in FIG. 3 can be integrated inorder to more clearly identify differences between the profiles. Theintegrated PSD profiles are shown in FIG. 4. Profiles 41′, 42′, 43′, and44′ in FIG. 4 represent the integrated versions of profiles 41, 42, 43,and 44 in FIG. 3. Even through profiles 41-44 in FIG. 3 were essentiallyindistinguishable between frequencies of 0 and 15 KHz, the integratedprofiles in FIG. 4 can more easily be identified with respect to eachother. Profiles 41′ and 42′ represent good gears, whereas profile 43′represents a spalled gear set and profile 44′ represents a bad gear setwith a chipped tooth.

In actual operation, the present invention would develop a referenceprofile, or magnitude, for an undamaged and unspalled gear set. Thatreference magnitude would be similar to profiles 41′ and 42′ in FIG. 4.In actual practice, the reference profile would be developed byaveraging a preselected number of profiles taken with gear sets that areknown to be undamaged and unspalled. That reference profile would thenbe used for later comparison to more recent profiles taken during theoperation of the apparatus, such as a marine propulsion system. If aprofile similar to 43′ was monitored, the present invention coulddiagnose the marine propulsion system as having a spalled gear thatrequires attention in the near future. A profile similar to 44′,however, would represent a damaged gear set, such as with a chippedtooth, and would necessitate immediate action by the operator. Bothconditions, represented by profiles 43′ and 44′, would result in analarm condition that would notify the operator of a potential futurefailure. Since the present invention is able to detect the differencebetween a spalled gear set 43′ and a chipped tooth gear set 44′,specific alarms could be tailored to more particularly inform theoperator of the diagnosed malfunction.

In a marine propulsion system, various different components cansimultaneously exhibit precursors of potential future failures. Forexample, marine propellers can be damaged if they are caused to impactsubmerged obstacles, such as rocks or floating debris. A damagedpropeller will induce vibrations in the gearcase of a marine propulsionsystem. It is necessary that a monitoring system be able to distinguishbetween signals received as a result of a spalled or bad gear set fromsignals received as a result from a damaged propeller. FIG. 5 representssix profiles of integrated power spectral densities. Profile 51 is theresult of a good gear set combined with an undamaged propeller. Profile52 is the result of a spalled gear set with a good propeller. Profile 53is the result of a bad gear set with a good propeller. As can be seen,profiles 51, 52, and 53 differ by a slight, but measurable, magnitudethat allows the present invention to distinguish a good gear set 51 froma spalled gear set 52 or a bad gear set 53 when the three conditionsexist with an undamaged propeller.

With continued reference to FIG. 5, profile 54 represents a good gearset run with a damaged propeller, profile 55 represents a spalled gearset with a damaged propeller, and profile 56 represents a bad gear setwith a bad propeller.

With continued reference to FIG. 5, it can be seen that the use of thePSD profiles by the present invention allows the detection of precursorsof future failure even when combined precursors are present in thesystem. For example, the lower profiles, 51-53, demonstrate that spalledand bad gear sets can be identified and distinguished from each otherwhen the propeller is undamaged. The upper three profiles, 54-56, showthat even with a damaged propeller the spalled gear set and the bad gearset can be distinguished from a good gear set with an integrated PSDprofile.

FIG. 6 shows the PSD profiles for an undamaged propeller 61 and adamaged propeller 62, both propellers being associated with good gearsets. At frequencies between 0 and 1 KHz, the damaged propeller 62 hassignificantly higher energy and can easily be detected by the method ofthe present invention. The profiles shown in FIG. 5 and described aboveare integrated PSD profiles. FIG. 7 shows the power spectral densityprofiles for the same combinations of damaged and undamaged propellerscombined with good gear sets, spalled gear sets, and bad gear sets.However, the profiles shown in FIG. 7 are not integrated. Profile 71 isa bad gear set with an undamaged propeller, profile 72 is a spalled gearset with an undamaged propeller, and profile 73 is a good gear set withan undamaged propeller. Also shown in FIG. 7 are the profiles for a badgear set with a damaged propeller 74, a good gear set with a damagedpropeller 75, and a spalled gear set with a damaged propeller 76. Thegrouping identified by oval 78 all involve a damaged propeller, whereasthe grouping identified by oval 79 all have undamaged propellers.

The power spectral density profiles described above relate toinformation obtained from an accelerometer. It should be understood thatthe power spectral density profiles can comprise other types of datarepresenting various indicators parameters. For example, ignition systemfeedback has been researched in the automotive industry for severaldecades. Much of this research utilizes micro-processors, included inautomotive control systems, that are used in diagnostic applicationsrelating to misfire detection and diagnostics. Relative engine load,air/fuel mixture abnormalities, and misfire detection can all bedetermined by ignition power spectral densities.

FIG. 8 shows three PSD profiles relating to a normally operatingignition system. Profile 81 represents an engine running at idle speed,profile 82 represents an engine running at 1800 RPM, and profile 83represents an engine running at 4000 RPM. Fouled or worn spark plugs cancause an ignition system to run sub-optimally. The energy transferred tothe spark gap of a spark plug is thereby reduced. In the case of fouledspark plugs, the ignition energy is shorted between the center andground electrodes. Typically, the plug is not completely shorted andsome spark does occur, but spark is typically tracking on the surface ofthe spark plug core and is not in a suitable location for a properinitiation of combustion. In the case of a worn spark plug, the gap hasbeen increased substantially and the demand voltage is increasedproportionally with the increased gaps. The ignition coil fires acrossthis larger gap, but at a shorter duration due to the increase inrequired voltage. These scenarios can be observed at relatively lowfrequencies. For example, FIG. 9 shows three PSD profiles. In FIG. 9,the power spectral density profiles represent a normal spark plug 91, aworn spark plug 92, and a fouled spark plug 93. As can be seen in FIG.9, the worn and fouled spark plugs, 92 and 93, can easily bedistinguished from a normal spark plug 91 even at the relatively lowfrequency range of 0 to 200 KHz.

Using secondary ignition energy, the present invention is also able todetect a failed ignition coil, a stuck injector, and a degradedinjector. In FIG. 10, a normal secondary ignition power spectral densityprofile 101 is compared to various types of faults. A bad coil 102 isobviously distinguishable from the good coil 101. A stuck injector 103shows a higher energy than the good coil 101 within the range of 0 to 5KHz. Profile 105 represents a “start of air” parameter for a direct fuelinjector that was intentionally retarded by 7 degrees to simulate a weakinjector which does not have the proper electromechanical response time.Power spectral density profile 104 represents an overly lean mixture offuel and air. In FIG. 10 the various profiles, except the bad coil 102,are relatively similar to each other and not easily distinguished fromeach other. However, if the profiles in FIG. 10 are integrated, theyyield results shown in FIG. 11. The normal ignition profile 111 caneasily be distinguished from the various fault conditions. For example,the stuck air injector 113 and the overly lean mixture 114 aremeasurably lower than the normal PSD profile 111. In addition, thesimulated degraded injector, which is actually simulated by retardingthe start of air parameter by 7 degrees, is represented by line 115. Thebad coil 112 is the lowest power spectral density profile in FIG. 11. Ascan be seen, the integrated profiles in FIG. 11 are easilydistinguishable from each other.

A fuel pressure transducer can also be used by the present invention todetect a stuck fuel injector. A struck fuel injector results inmiddle-to-high frequency disturbance in the fuel rail of a fuel injectedengine. Because the pressure fluctuation frequency is generally relatedto engine speed, the energy seen in the pressure fluctuations at 4000RPM is more than 10 times greater than that seen at idle.

In FIG. 12, the four power spectral density profiles represent a normalinjector at idle 121, a stuck injector at idle 122, a normal injector at4000 RPM 123, and a stuck injector at 4000 RPM 124. As can be seen, thetwo traces at idle are generally similar to each other as are the twotraces at 4000 RPM. Although distinctions can be seen between a goodinjector and a stuck injector at both engine speeds, they are not aseasily detected as they are when the profiles in FIG. 2 are integrated.

FIG. 13 represents the integral profiles of the power spectral densitiesrepresented in FIG. 12. The good injector at idle speed (referencenumerals 121 and 131) and the stuck injector at idle speed (referencenumerals 122 and 132) are generally similar to each other, even whenintegrated as represented in FIG. 13. However, the stuck injector 134 iseasily discernible from the good injector 133.

Air rail pressure can also be used by the present invention to sense adegraded or struck air injector. A degraded air injector has beensimulated by retarding the start of air injector by 7 degrees, asdescribed above. FIG. 14 represents the power spectral density of theair rail pressure signal when the engine is operating at idle speed. Thenormal air injector 141 and the degraded air injector 142 appear to begenerally similar to each other in FIG. 14. A stuck air injector 143 canbe distinguished from the other two in FIG. 14, but only at frequenciesgreater than 5 KHz. It becomes significantly easier to distinguish thesethree profiles from each other if the power spectral densities areintegrated, as represented in FIG. 15. The struck air injector 143 caneasily be distinguished from both the normal air injector 141 and thedegraded air injector 142 when the power spectral densities areintegrated. If the reference value for this particular indicatorparameter is profile 141, the present invention can both detect andidentify the degraded air injector 142 and the struck air injector 143.

Air injector voltage can also be monitored for the purpose ofdistinguishing a properly operating air injector from one that isstruck. FIGS. 16 shows two voltage traces that comprise 1000 samplestaken over a period of approximately ten milliseconds. The good injectoris represented by trace 161 and the stuck injector is represented bytrace 162. The time domain trace shown in FIG. 16 represents the airinjection voltage as it is initially fired and limited to three amperesand then held between 1 and 2 amperes for the duration of the injectionprocess. The current limiting is achieved by a monostable chopper,resulting in the chop near the bottom of the voltage waveforms. Itshould be noticed that the increased amplitude of the fly-back voltageis evident in the struck injector 162. The increased voltage may be aneffect of the reluctance at the initial condition, whereas thereluctance decreases in the case of the properly operating injector 161.

With reference to FIG. 17, the power spectral density for the goodinjector 171 allows the present invention to recognize the existence ofa struck injector 172. Even at relative low frequencies below 5 KHz, thedifference is detectable. Therefore, the power spectral density of theair injector voltage allows the present invention to use this indicatorparameter as a precursor of a potential future failure.

FIG. 18 shows a representative flow chart that can be followed toperform the steps of the present invention. From the start block 181,the micro-processor first determines if the run time at the preselectedoperating conditions has exceeded 20 hours of learn mode. It should beunderstood that the 20 hour period is hypothetical for purposes of thedescription and is not limiting to the present invention. What thismeans is that the first 20 hours of operation at any particular set ofoperating conditions, such as might be defined by the operating speed ofthe engine and the load on the engine, is used to calculate a referencemagnitude that will later be used as a template against which subsequentmagnitudes of the indicator parameter will be compared. As will bedescribed in greater detail below, the present invention also uses amethod for characterizing the operation of an apparatus, such as amarine propulsion system, and that method incorporates steps thatdevelop a profile of usage of the apparatus as a function of 1 or moreoperating conditions. If the system is still in the learning mode forthe present set of operating conditions under which the apparatus isoperating, the power spectral density is observed, at functional block182, and it is recorded as a function of engine speed and load. This isrepresented by functional block 183 which records the time at the loadand RPM. Until a reference magnitude of the power spectral density canbe calculated for 20 hours running time, an absolute threshold is used.This comparison of the current power spectral density and the absolutethreshold is made at functional block 184. If the PSD exceeds theabsolute threshold, a message is provided to the user at functionalblock 185.

With continued reference to FIG. 18, if the system has operated for morethan 20 hours at the particular combination of operating conditions, asdetermined by functional block 186, the power spectral density is againtaken at functional block 187 and compared to a reference magnitude ofthe power spectral density as determined by a particular relationshipdefined at functional block 188. If it exceeds the threshold, a messageis provided at functional block 189 to notify the operator.

With continued reference to FIG. 18, it can be seen that the powerspectral density for a selected indicator parameter, such as anaccelerator output signal, is periodically measured. During the first 20hours of operation at any particular set of operating conditions, theperiodic measurements are used to determine a reference magnitude thatwill be used in comparison to subsequent power spectral densities forthe indicator parameter. During that initial 20 hour period of time,preset absolute thresholds will be used to determine an improperoperation of the indicator parameter. After a reference magnitude, orprofile, is calculated for the indicator parameter, the referencemagnitude is used for these comparisons.

Although functional block 188 shows that the power spectral density iscompared to a value that is 50% greater than the maximum power spectraldensity recorded by block 183, it should be understood that this is onlyone of many comparison algorithms that can be used. These values can becalibrated, depending on the sensing distribution.

Throughout the description of the preferred embodiment, reference hasbeen made to the development of a usage profile for the apparatus as afunction of one or more operating conditions. It has been found thatengine speed and engine load are two particularly useful operatingconditions that can be used for a basis for the recordation andcomparisons described above. It has also been determined that comparisonof the most currently read power spectral density (PSD) for an indicatorparameter need only be compared to reference profiles of the powerspectral density for that indicator parameter at certain nodes orcombinations of operating parameters. As an example, if an engine of amarine propulsion system had never been operated above a speed of 5000RPM, hypothetically, it would not be wise to determine the proper orimproper operation of an indicator parameter with data obtained at thatseldom used engine speed. Furthermore, if the engine of a marinepropulsion system is seldom operated above 400 ft lbs. of torque, itwould similarly be unwise to make any decisions regarding the proper orimproper operation of an indicator parameter at that load. More simplystated, it is not wise to make decisions regarding the proper orimproper operation of an indicator parameter at operating conditionsthat are not commonly used ones for the marine propulsion system orother apparatus being monitored. In order to further perfect thesetechniques described above, the present invention selects one or moreoperating characteristics and records the time at which the apparatus isoperated at the various combinations of those operating characteristics.For example, FIG. 19 shows a time profile for the operating conditionsof engine speed, measured in RPM, and the load on the engine measured asfoot-pounds of torque. The surface plot of FIG. 19 represents theresults of this effort. As can be seen in FIG. 19, the most commonoperating condition of the apparatus is in the region of 3000 RPM and400 ft lbs. of torque. The second most common operating domain is in theregion between 3000 and 4000 RPM and between 0 and 100 ft lbs. oftorque.

With continued reference to FIG. 19, it can be seen that the subjectengine had not been operated significantly at engine speeds less than1000 RPM or greater than 5000 RPM. The present invention contemplatesthe use of a time threshold magnitude to determine whether or notsufficient usage of the apparatus at the particular combination ofoperating conditions has occurred. FIG. 20 shows the application of athreshold level of three minutes represented by the plane identified byreference numeral 201. When this threshold magnitude is applied to thesurface represented in FIG. 19, only three localized operatingconditions exceed the threshold. The largest peak 191 clearly exceedsthe threshold. Another peak 192 also clearly exceeds the threshold. Thethird peak 193 also exceeds the threshold 201, but by a lesser degree.According to one preferred embodiment of the present invention, onlydata representing the operating conditions coincident with the threepeaks shown in FIG. 2 would be used in the comparison represented byfunctional block 188 in FIG. 18. All other regions of the operatingconditions of the apparatus have insufficient usage durations to qualifythem for the purpose of being used to actually determine the referencepower spectral density profile which, as described above, is used as atemplate to determine the acceptable of subsequently taken powerspectral densities. As the apparatus is continually operated, otherpeaks in the surface shown in FIG. 19 will develop and grow beyond thethreshold represented by plane 201.

If the present invention is monitoring a marine propulsion system, themicro-processor would continually measure the engine speed and the loadon the engine to determine where in FIG. 19 the operating time should beaccumulated. The power spectral densities for various indicatorparameters would be measured and stored by the micro-processor as thevarious operating nodes grow in intensity as peaks in FIG. 19. It isassumed that many combinations of operating characteristics, measured byengine speed and engine load will occur only rarely and may neverachieve the threshold magnitude 201. The present invention contemplatesthis and assumes that any particular marine propulsion system willexperience an operational history that comprises numerous nodes, such aspeaks 191-193, in its commonly used areas of operating characteristicswhile experiencing very low usage rates at other operatingcharacteristics. By using a methodology as described above inconjunction with FIGS. 19 and 20, the present invention is able to useactual operational data developed from actual operating results forindicator parameters of the apparatus. This precludes the necessity ofusing artificial parameters that may or may not be applicable for anyparticular system. The present invention uses actual operational historyto determine what the normal operating range of an indicator parameteris for each particular marine propulsion system. It also monitors theusage time at each of the combinations of operating parameters to makesure that the reference magnitudes are determined based on many repeatedsamples at operating conditions that are normal for the apparatus. Atlater times, after the several operational peaks, 191-193, aredeveloped, the micro-processor only uses reference power spectraldensities, or integrals thereof, determined for those particularoperational nodes.

FIG. 21 shows a flow chart that can be used by a micro-processor toperform the steps of the present invention as described above inconjunction with FIGS. 19 and 20. The flow chart begins by assuring thatthe engine is in a steady state, at least with regards to engine speedand engine load. This is provided at functional block 211. The histogramcluster, as represented by FIG. 19, is updated at functional block 212and a determination is made at functional block 213 whether or not atotal of 20 hours of learning mode has elapsed. If the run time is lessthan 20 hours, a power spectral density reading is taken at functionalblock 214, a table of this current PSD and previously monitored PSD'sare sorted at functional block 215 and a determination is made atfunctional block 216 to determine whether or not the most recently takendata exceeds a preselected threshold. If it does, a message is providedto the user at functional block 217 and if it does not, the systemreturns to functional block 211. If the run time is greater than 20hours, as determined by functional block 213, the previously taken powerspectral densities are sorted at functional block 218 and it isdetermined whether or not a new combination of operationalcharacteristics has occurred. For example, if the engine is detected asoperating at an engine speed and an engine load that had not beforeoccurred, as determined by functional block 219, functional blocks 220,221, 222, and 223 are performed to recognize the existence of a new setof operating characteristics and making sure that the system correctlylogs that new occurrence into the existing database. The newly takenpower spectral density is then stored, at functional block 224 and acomparison is made at functional block 225 to a preselected threshold.If the comparison shows that the threshold has been exceeded, a messageis provided to the user at functional block 226 and the system returnsto functional block 218.

Several embodiments of the present invention have been described above.One embodiment relates to a method for characterizing the operation ofan apparatus. This is described above in conjunction with FIGS. 19, 20,and 21. It comprises the steps of monitoring the magnitude of a firstoperating condition of an apparatus, which can be engine speed or engineload or any other operating condition that relates to a preselectedindicator parameter. The indicator parameter is periodically measuredduring a time when the apparatus is operating at the first magnitude ofthe first operating condition. For example, the power spectral densityor integral of a power spectral density of a signal obtained from aaccelerometer can be taken and stored as a function of a first operatingcondition which can be, for example, 3000 RPM at 300 ft lbs. of torque.The engine speed and engine load combine to identify a particularoperating condition and the measurement of the indicator parameter isstored as a function of that particular combination for later reference.A plurality of these measurements of the indicated parameter are storedand used to determine a reference magnitude of the first indicatorparameter. As an example, a plurality of these measurements of the firstindicator parameter can be averaged to calculate the referencemagnitude. Alternatively, they can be used in a regression formula todetermine the norm of the plurality of readings. Other mathematicalmethods can also be used to select a reference magnitude from theplurality of measured magnitudes of the indicator parameter. Theindicator parameter, as described above, can be a power spectral densityor the integral of a power spectral density for any one of a number ofdifferent signals, including an accelerometer output, the output of apressure sensor, or a voltage output from a system such as an ignitionsystem. The reference magnitude is stored by the present invention forlater comparison to subsequent readings. The present invention alsocompares the accumulative duration of time to a predetermined thresholdmagnitude. The accumulated duration of time can include all operatingtimes at all operating conditions or, alternatively, it can include apredetermined threshold of time at the particular operating conditiondefined by the current engine speed and engine load. The differencebetween the most recently taken magnitude of the indicator parameter andthe stored reference magnitude of the indicator parameter is thencalculated. If this difference exceeds a preselected value, a signaloutput can be provided to warn an operator of this occurrence.

The present invention also contemplates the use of a particularfrequency range of a power spectral density for purposes of comparing areference magnitude to a subsequent value of the indicator parameter.

Although the present invention has been described with particularspecificity and illustrated to describe several preferred embodiments,it should be understood that other embodiments and variations thereofare also within its scope.

What is claimed is:
 1. Apparatus for prognosticating a condition of amarine propulsion system, comprising: means for determining a referencemagnitude of an indicator parameter under a first set of preselectedoperating conditions; means, connected in signal communication with saiddetermining means, for storing said reference magnitude of an indicatorparameter; means for measuring a current magnitude of said indicatorparameter under said first set of preselected operating conditions, saidcurrent magnitude being measured subsequent to said reference magnitudebeing determined; means, connected in signal communication with saidstoring means, for comparing said reference and current magnitudes; andmeans, connected in signal communication with said comparing means, fordetecting a change in said condition of said marine propulsion system.2. A method for prognosticating a condition of a apparatus, comprising:determining a reference magnitude of an indicator parameter under afirst set of preselected operating conditions, said apparatus being amarine propulsion system; storing said reference magnitude of anindicator parameter; measuring a current magnitude of said indicatorparameter under said first set of preselected operating conditions, saidcurrent magnitude being measured subsequent to said reference magnitudebeing determined; comparing said reference and current magnitudes; anddetecting a change in said condition of said apparatus as a function ofsaid comparing step.
 3. The method of claim 2, further comprising:repeating said measuring, comparing, and detecting steps at apredetermined frequency.
 4. The method of claim 2, further comprising:determining said reference magnitude of each of a plurality of indicatorparameters under an associated first set of preselected operatingconditions for each of said plurality of indicator parameters; storingsaid reference magnitude of each of said plurality of indicatorparameters; measuring said current magnitude of each of said pluralityof indicator parameters under said associated first set of preselectedoperating conditions, said current magnitude of each of said pluralityof indicator parameters being measured subsequent to said referencemagnitude of each of said plurality of indicator parameters beingdetermined; comparing each of said reference magnitudes to itsassociated current magnitude; and detecting a change in said conditionof said apparatus as a function of said comparing step.
 5. The method ofclaim 2, wherein: said indicator parameter is an output from anaccelerometer.
 6. The method of claim 2, wherein: said indicatorparameter is an output from a fuel pressure sensor.
 7. The method ofclaim 2, wherein: said indicator parameter is an output from an ignitionsystem.
 8. The method of claim 2, wherein: said indicator parameter isan output from an air pressure sensor.
 9. The method of claim 2 wherein:said marine propulsion system comprises a gear case, a fuel supplysystem, an ignition system, an oil delivery system, and an air deliverysystem.
 10. The method of claim 2, wherein: said indicator parameter isa power spectral density of a preselected variable.
 11. The method ofclaim 2, wherein: said indicator parameter is a plurality of valuesrepresenting power spectral density of a preselected variable for aplurality of frequencies.
 12. The method of claim 2, wherein: saidindicator parameter is the integral of a power spectral density of apreselected variable.
 13. The method of claim 2, wherein: said first setof preselected operating conditions comprise a magnitude of the speed ofan engine and a magnitude of a load on said engine.
 14. A method forprognosticating a condition of a apparatus, comprising: determining areference magnitude of each of a plurality of indicator parameters underan associated first set of preselected operating conditions for each ofsaid plurality of indicator parameters; storing said reference magnitudeof each of said plurality of indicator parameters; measuring a currentmagnitude of each of said plurality of indicator parameters under saidassociated first set of preselected operating conditions, said currentmagnitude of each of said plurality of indicator parameters beingmeasured subsequent to said reference magnitude of each of saidplurality of indicator parameters being determined; comparing each ofsaid reference magnitudes to its associated current magnitude; detectinga change in said condition of said apparatus as a function of saidcomparing step; and repeating said measuring, comparing, and detectingsteps at a predetermined frequency.
 15. The method of claim 14, wherein:said apparatus is a marine propulsion system which comprises a gearcase.
 16. The method of claim 14, wherein: said indicator parameter is apower spectral density of a preselected variable.
 17. The method ofclaim 14, wherein: said indicator parameter is a plurality of valuesrepresenting power spectral density of a preselected variable for aplurality of frequencies.
 18. The method of claim 14, wherein: saidindicator parameter is the integral of a power spectral density of apreselected variable.
 19. The method of claim 14, wherein: said firstset of preselected operating conditions comprise a magnitude of thespeed of an engine and a magnitude of a load on said engine.